Project Summary Multiple organ dysfunction syndrome (MODS), consequent to trauma, is a major underlying cause of mortality in intensive care units. Research supported by the previous funding cycle has revealed fundamental mechanisms that modulate inflammation and metabolic recovery during MODS through activation of the AMP-activated protein kinase (AMPK), a central regulator of cellular energy homeostasis and mitochondrial quality control. This work has now logically progressed to investigating the molecular machinery that is initiated by humanin, a mitochondrial derived peptide with putative cytoprotective properties in aging. By using a clinically relevant murine model of hemorrhagic shock, we have observed that changes in plasma humanin levels correlate with AMPK failure and severity of organ injury in mature and old, but not young mice. Furthermore, administration of the potent humanin analogues, humanin-G (HNG) and colivelin, afforded beneficial effects in an AMPK- dependent and -independent manner, also involving the signal transducer and activator of transcription 3 (STAT3). The present proposal seeks to understand how humanin participates in these signaling pathways to improve mitochondrial function and promote organ metabolic recovery. We will conduct a multidisciplinary investigation to dissect these cross-talks by employing both genetic and pharmacological approaches of loss-of- function of AMPK and STAT3, and by using humanin analogues in model systems of in vivo integrated physiology combining molecular profiles and functional measurements. A special consideration will be given to the biological variables of age and sex that are known to affect progress of organ injury and outcomes in critically ill patients. Specifically, we will determine whether: 1) the spatio-temporal kinetics of humanin during hemorrhagic shock correlate with MODS; 2) humanin has a biological role in modulating the pathophysiology of MODS; 3) humanin contributes to the regulation of mitochondrial function by AMPK-independent metabolic pathways or AMPK- independent signaling through modulation of STAT3 subcellular localization and activation. The successful completion of this work will reveal fundamental stress-responsive circuits of mitochondrial quality control and identify new therapeutic targets that can have a major impact in clinical intervention.